1. Field of the Invention
This present invention relates generally to a method of image de-interlacing, and more particularly to a selection methodology of de-interlacing algorithm of dynamic image in accordance with performance of player system and encoding condition of input image.
2. Description of the Prior Art
The trend of digitalization has formed as the application of multimedia technology develops; therefore a video/audio player and display system has to include the function of transmitting analog signals to digital signals. There are two kinds of scanning standard of analog television at present, i.e. National Television System Committee (NTSC) and Phase Alternation by Line (PAL). Standard of NTSC is used in Japan or the US, according to which a frame is formed by 525 scanning lines i.e. 525 scanning lines are called a frame, which means the frame is displayed repeatedly at the speed of 30 frames per second. Yet 525 scanning lines that form a frame are not finished in only one scanning. The frame is displayed by scanning one line and then the line following the next line. In other words, after the first line is scanned, the third line is scanned rather than the second line, and then the fifth, seventh, to the 525th line respectively. Then the scanning process returns to the second line and repeats, in the following are the fourth, sixth, eighth, etc. Therefore the smooth and clear frame displayed is actually constituted by an odd number, an even number, and then an odd number, the formatting method of which is called “double-space scanning” or “interlacing”.
Details described, an interlaced video signal is composed of two fields, each of the two fields containing odd lines or even lines of the image. In the process of image capture, camera will output odd lines of image on instant basis and output even lines of image after 16.7 milliseconds. Amid process of outputting odd lines and even lines of the image, a temporal shift will occur, wherein the temporal shift should be positioned in the system of frame-based processing. For a still frame, a good one can be obtained with this method. But for a frame with motion, the image will become blurred since serration will occur on the edge of the image called feathering. Besides, since field of odd lines and field of even lines are formed by only half amount of scanning lines (262.5 lines), each field of odd lines and field of even lines only has half of the resolution the original image has. Each field of odd lines and field of even lines is displayed at the speed of 60 fields per second. Such frame will not appear to have motion artifacts to men's eyes, but if the frame is enlarged, the scanning lines will appear thick and the frame will become blurred.
The disadvantages of “interlacing scanning” described above can be eliminated by a technique called “progressive scan”. In progressive scan, the first, second, third, to the 525th line are scanned in order and displayed at the speed of 60 frames per second. Therefore its scanning speed is twice the scanning speed of “interlacing” and the frame is displayed on the monitor with 525 scanning lines, which makes the frame fine and clear, which being the best merit of “progressive scan”. Therefore, most of the developed video and audio equipment at present has used this method for scanning and displaying.
However, current video signal of NTSC system uses mainly the method of “interlacing” so far. Therefore, if a frame constituted by interlacing is displayed by a display system using a progressive scan: for instance, when a DVD film edited by interlacing is directly broadcast and displayed on HDTV, only frame of odd lines and frame of even lines can be displayed and the resolution of image will be worse. To solve this problem, the technique of “de-interlacing” should be used. In other words, de-interlacing is a method to convert interlacing to a progressive scan. The misalignment of image should be amended so that a progressive image that can satisfy the vision can be produced.
Besides, the technique of dynamic image compression uses mainly standard of Motion Pictures Experts Group (MPEG) compression. In the process of MPEG compression (or encoding), three different methods are used to compress each frame: Intra-frame (I-frame), Bi-directional frame (B-frame) and Predicted frame (P-frame). Wherein the I-frame cuts a frame as macro block of a 16×16 pixel for processing, each macro block is composed of a luminance block (i.e. Y block) of four 4×4 pixels, a Cr block of one 8×8 pixel and a Cb block of one 8×8 pixel. And the I-frame has no need to put its relation with other frames in consideration since a complete frame is saved. P-frame takes former I-frame as reference frame, wherein the redundant part of frame is not saved and only different part of frame is saved. The principle of B-frame is the same as that of P-frame, the only difference is that B-frame can take former I-frame or P-frame as reference and can also take latter P-frame as reference.
Current Video CD (VCD) or multi-function DVD is edited by images of film using interlacing scanning, therefore a frame is constituted by interlacing when playing. To prevent some problem of a frame constituted by interlacing displayed by the display system using progressive scan, interlacing scanning is necessary. However, in the process of editing a VCD or DVD film, in accordance with some video/audio which use standard of Joint Photographic Experts Group (JPEG) or those films edited by using I-frame of MPEG compressing standard in one disc and films without compression, since dynamic image might only include encoding information of I-frame or only include information of dynamic image, it can't detect motion vectors when playing such kind of film in the video/audio player system and therefore encoding incompatible problem occurs. Consequently, it can't play such kind of film without motion vectors in the player system and it's not convenient for users. Besides, in accordance with a video/audio player system without providing a selection mechanism, when it's restricted for the limit of hardware performance such as insufficient memory or not enough bandwidth, the de-interlacing algorithm in the hardware system requiring more requirements cannot execute. And it cannot display with best image quality for lack of the selection mechanism of de-interlacing algorithm.